The invention relates to the so-called tray sealers, i.e. machines which seal with a covering film tubs or trays filled with a product to be packaged, such as a food product. The document cited as the closest prior art to this invention is the published U.S. patent application No. US 2004/098947, which envisages placing downstream of the sealing and cutting station a pair of complementary-shaped rollers which are used to pincer the longitudinal edges of the film exiting from said station, which are divergent to each other in the direction of advance of said film and which are mounted on freely stepped wheels, so as to allow solely advance of said film. This solution is problematic, since it requires a specific action of insertion of the edges of the film between said rollers and subjects the film substantially to a single transversal stretching action, entirely equivalent to the one performed by said spreader roller.
Also cited as the prior art documents are EP 1 038 773 of 27 Sep. 2000, and DE 10 2007 021517 of 14 Aug. 2008.